The present invention relates to intravenous fluid infusion apparatus and, in particular, to such infusion apparatus capable of administering variable volumes of the same or a different fluid to a patient.
Conventional apparatus for intravenous infusion of fluids utilizes an elevated fluid receptacle connected by flexible conduit or tubing to the hub of a catheter or needle inserted into the patient. A flow control device regulates the rate of fluid flow through the tubing and a metering device, called a drop chamber, provides a means to measure the fluid flow rate. A conventional drop chamber comprises a drop tube having a single drop forming orifice that separates the fluid stream into a series of individual droplets that then fall by gravity through a hollow transparent body to allow the droplets to be monitored. By knowing the volume of each droplet, which is determined by the size of the drop orifice and is labeled on the packaging of the apparatus, the rate of fluid administration can be determined by counting the rate of droplet formation or drop rate. The flow control device is adjusted while the drop rate is monitored to control the fluid administration rate.
The viscosities of different parenteral fluids vary greatly. For example, aqueous base solutions have a low viscosity while whole blood and blood plasma have relatively high viscosities. As a result, it is necessary to select a drop chamber having a drop tube orifice that corresponds to the droplet volume appropriate for the fluid used. A 60 drop per cubic centimeter orifice, suitable for administering saline solution, would clog if attempted to be used for administering blood. At other times, a very small orifice is required to administer very small amounts of fluid because of the concentration of the medicine in the solution and the necessity of accurate infusion.
Because of the foregoing limitation, it is necessary to change to a different drop chamber, having an appropriate drop orifice size, whenever it is necessary to administer a fluid having a viscosity significantly different from the one currently being administered. This change in apparatus, which is sterile, increases the risk of contaminating the patient. In addition, valuable time is spent in selecting the appropriate drop chamber, in reconnecting the apparatus and in evacuating air from the apparatus. Further, if the wrong drop tube is selected in an emergency situation, the apparatus must be disconnected and the proper apparatus connected. Changing of the apparatus, as with any medical procedure, may be stressful to a patient and is therefore best kept to a minimum. Finally, increased expenses are associated not only with the use of multiple apparatus sets for each patient but also with the necessity to inventory several different orifice size drop chambers.
Many medical procedures require a change in the fluid being intravenously administered to the patient. For example, a trauma patient is stabilized in an ambulance using an aqueous base solution. Once the trauma patient arrives at the treatment facility, and their blood type can be determined, whole blood or blood plasma may then be administered, if indicated. As another example, major surgery such as coronary artery by-pass, requires that whole blood or blood plasma be administered to the patient during the actual procedure and aqueous base solution administered after the patient is sutured. Should hemorrhaging develop and additional surgery be required, the patient must be taken off of the glucose or saline solution and again be administered whole blood or blood plasma.